1. Field of the Invention
The present invention relates to an auto focus device, and more particularly, to an auto focus device that easily sets the position of an AF (auto focus) frame indicating a desired focus range in an auto focus system.
2. Description of the Related Art
In general, a contrast method has been used as an auto focus (hereinafter, referred to as AF) method. In the contrast method, the contrast of the image of an object captured by an imaging device is detected from the image signals (video signals) of the image of the object, and the focus of an imaging lens (focus lens) is controlled such that the contrast is the highest. In this way, focusing is automatically performed in the best focus state.
In contrast-type AF, in many cases, the imaging range (image capture range) of a camera is not the AF target range, but the target is just an object in one portion of the imaging range. For example, among the image signals of the image of the object effectively captured by the imaging device, the image signals in a predetermined range, which are an AF target, are extracted and focusing is controlled on the basis of the extracted image signals in the range such that the contrast of the image becomes the highest. In this way, the AF target is limited to the object in one portion of the imaging range.
In the specification, the AF target range is referred to as an AF area, a frame indicating the range of the AF area (the outline of the AF area) is referred to as an AF frame.
An AF system has been proposed which sets the position, size, or shape of the AF area. In the system, a cameraman operates, for example, a joystick to move the AF frame such that the AF frame overlaps an object in focus. That is, the cameraman performs a manual focus operation (for example, see JP-A-2007-25595).
However, it is inconvenient to set the AF area (AF frame) using a manual operation, as in the related art. Therefore, it is convenient that the AF frame be automatically set. However, when the AF frame is automatically set, there is a problem in that it is difficult to set the AF frame at the cameraman's intended position, and automatically setting the AF frame to a desired position is not easy.